// /*
//   Copyright (c) 2013, 2018, Oracle and/or its affiliates. All rights reserved.

//   The MySQL Connector/J is licensed under the terms of the GPLv2
//   <http://www.gnu.org/licenses/old-licenses/gpl-2.0.html>, like most MySQL Connectors.
//   There are special exceptions to the terms and conditions of the GPLv2 as it is applied to
//   this software, see the FOSS License Exception
//   <http://www.mysql.com/about/legal/licensing/foss-exception.html>.

//   This program is free software; you can redistribute it and/or modify it under the terms
//   of the GNU General Public License as published by the Free Software Foundation; version 2
//   of the License.

//   This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY;
//   without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
//   See the GNU General Public License for more details.

//   You should have received a copy of the GNU General Public License along with this
//   program; if not, write to the Free Software Foundation, Inc., 51 Franklin St, Fifth
//   Floor, Boston, MA 02110-1301  USA

//  */

// package com.mysql.jdbc;

// import java.lang.ref.PhantomReference;
// import java.lang.ref.Reference;
// import java.lang.ref.ReferenceQueue;
// import java.util.Set;
// import java.util.concurrent.ExecutorService;
// import java.util.concurrent.Executors;
// import java.util.concurrent.ThreadFactory;
// import java.util.concurrent.locks.Lock;
// import java.util.concurrent.locks.ReentrantLock;

// import com.networknt.utility.ConcurrentHashSet;

// /**
//  * This class implements a thread that is responsible for closing abandoned MySQL connections, i.e., connections that are not explicitly closed.
//  * There is only one instance of this class and there is a single thread to do this task. This thread's executor is statically referenced in this same class.
//  */
// public class AbandonedConnectionCleanupThread implements Runnable {
//     private static final Set<ConnectionFinalizerPhantomReference> connectionFinalizerPhantomRefs = new ConcurrentHashSet<>();
//     private static final ReferenceQueue<MySQLConnection> referenceQueue = new ReferenceQueue<MySQLConnection>();

//     private static final ExecutorService cleanupThreadExcecutorService;
//     static Thread threadRef = null;
//     private static Lock threadRefLock = new ReentrantLock();
//     private static boolean abandonedConnectionCleanupDisabled = Boolean.getBoolean("com.mysql.cj.disableAbandonedConnectionCleanup");

//     static {
//         if (abandonedConnectionCleanupDisabled) {
//             cleanupThreadExcecutorService = null;
//         } else {
//         // connectionFinalizerPhantomRefs = new ConcurrentHashMap<ConnectionFinalizerPhantomReference, ConnectionFinalizerPhantomReference>();
//         cleanupThreadExcecutorService = Executors.newSingleThreadExecutor(new ThreadFactory() {
//             public Thread newThread(Runnable r) {
//                 Thread t = new Thread(r, "mysql-cj-abandoned-connection-cleanup");
//                 t.setDaemon(true);
//                 // Tie the thread's context ClassLoader to the ClassLoader that loaded the class instead of inheriting the context ClassLoader from the current
//                 // thread, which would happen by default.
//                 // Application servers may use this information if they attempt to shutdown this thread. By leaving the default context ClassLoader this thread
//                 // could end up being shut down even when it is shared by other applications and, being it statically initialized, thus, never restarted again.

//                 ClassLoader classLoader = AbandonedConnectionCleanupThread.class.getClassLoader();
//                 if (classLoader == null) {
//                     // This class was loaded by the Bootstrap ClassLoader, so lets tie the thread's context ClassLoader to the System ClassLoader instead.
//                     classLoader = ClassLoader.getSystemClassLoader();
//                 }

//                 t.setContextClassLoader(classLoader);
//                 return threadRef = t;
//             }
//         });
//         cleanupThreadExcecutorService.execute(new AbandonedConnectionCleanupThread());
//         }
//     }

//     private AbandonedConnectionCleanupThread() {
//     }

//     public void run() {
//         for (;;) {
//             try {
//                 checkThreadContextClassLoader();
//                 Reference<? extends MySQLConnection> reference = referenceQueue.remove(5000);
//                 if (reference != null) {
//                     finalizeResource((ConnectionFinalizerPhantomReference) reference);
//                 }
//             } catch (InterruptedException e) {
//                 threadRefLock.lock();
//                 try {
//                     threadRef = null;

//                     // Finalize remaining references.
//                     Reference<? extends MySQLConnection> reference;
//                     while ((reference = referenceQueue.poll()) != null) {
//                         finalizeResource((ConnectionFinalizerPhantomReference) reference);
//                     }
//                     connectionFinalizerPhantomRefs.clear();
//                 } finally {
//                     threadRefLock.unlock();
//                 }
//                 return;
//             } catch (Exception ex) {
//                 // Nowhere to really log this.
//             }
//         }
//     }

//     /**
//      * Checks if the thread's context ClassLoader is active. This is usually true but some application managers implement a life-cycle mechanism in their
//      * ClassLoaders that is linked to the corresponding application's life-cycle. As such, a stopped/ended application will have a ClassLoader unable to load
//      * anything and, eventually, they throw an exception when trying to do so. When this happens, this thread has no point in being alive anymore.
//      */
//     private void checkThreadContextClassLoader() {
//         try {
//             threadRef.getContextClassLoader().getResource("");
//         } catch (Throwable e) {
//             // Shutdown no matter what.
//             uncheckedShutdown();
//         }
//     }

//     /**
//      * Checks if the context ClassLoaders from this and the caller thread are the same.
//      * 
//      * @return true if both threads share the same context ClassLoader, false otherwise
//      */
//     private static boolean consistentClassLoaders() {
//         threadRefLock.lock();
//         try {
//             if (threadRef == null) {
//                 return false;
//             }
//             ClassLoader callerCtxClassLoader = Thread.currentThread().getContextClassLoader();
//             ClassLoader threadCtxClassLoader = threadRef.getContextClassLoader();
//             return callerCtxClassLoader != null && threadCtxClassLoader != null && callerCtxClassLoader == threadCtxClassLoader;
//         } finally {
//             threadRefLock.unlock();
//         }
//     }

//     /**
//      * Shuts down this thread either checking or not the context ClassLoaders from the involved threads.
//      * 
//      * @param checked
//      *            does a checked shutdown if true, unchecked otherwise
//      */
//     private static void shutdown(boolean checked) {
//         if (checked && !consistentClassLoaders()) {
//             // This thread can't be shutdown from the current thread's context ClassLoader. Doing so would most probably prevent from restarting this thread
//             // later on. An unchecked shutdown can still be done if needed by calling shutdown(false).
//             return;
//         }
//         cleanupThreadExcecutorService.shutdownNow();
//     }

//     /**
//      * Performs a checked shutdown, i.e., the context ClassLoaders from this and the caller thread are checked for consistency prior to performing the shutdown
//      * operation.
//      */
//     public static void checkedShutdown() {
//         shutdown(true);
//     }

//     /**
//      * Performs an unchecked shutdown, i.e., the shutdown is performed independently of the context ClassLoaders from the involved threads.
//      */
//     public static void uncheckedShutdown() {
//         shutdown(false);
//     }

//     /**
//      * Returns true if the working thread is alive. It is alive if it was initialized successfully and wasn't shutdown yet.
//      * 
//      * @return true if the working thread is alive; false otherwise.
//      */
//     public static boolean isAlive() {
//         threadRefLock.lock();
//         try {
//             return threadRef != null && threadRef.isAlive();
//         } finally {
//             threadRefLock.unlock();
//         }
//     }

//     /**
//      * Tracks the finalization of a {@link MysqlConnection} object and keeps a reference to its {@link NetworkResources} so that they can be later released.
//      * 
//      * @param conn
//      *            the Connection object to track for finalization
//      * @param io
//      *            the network resources to close on the connection finalization
//      */
//     protected static void trackConnection(MySQLConnection conn, NetworkResources io) {
//         threadRefLock.lock();
//         try {
//             if (isAlive()) {
//                 ConnectionFinalizerPhantomReference reference = new ConnectionFinalizerPhantomReference(conn, io, referenceQueue);
//                 connectionFinalizerPhantomRefs.add(reference);
//             }
//         } finally {
//             threadRefLock.unlock();
//         }
//     }

//     /**
//      * Release resources from the given {@link ConnectionFinalizerPhantomReference} and remove it from the references set.
//      * 
//      * @param reference
//      *            the {@link ConnectionFinalizerPhantomReference} to finalize.
//      */
//     private static void finalizeResource(ConnectionFinalizerPhantomReference reference) {
//         try {
//             reference.finalizeResources();
//             reference.clear();
//         } finally {
//             connectionFinalizerPhantomRefs.remove(reference);
//         }
//     }

//     /**
//      * {@link PhantomReference} subclass to track {@link MysqlConnection} objects finalization.
//      * This class holds a reference to the Connection's {@link NetworkResources} so they it can be later closed.
//      */
//     private static class ConnectionFinalizerPhantomReference extends PhantomReference<MySQLConnection> {
//         private NetworkResources networkResources;

//         ConnectionFinalizerPhantomReference(MySQLConnection conn, NetworkResources networkResources, ReferenceQueue<? super MySQLConnection> refQueue) {
//             super(conn, refQueue);
//             this.networkResources = networkResources;
//         }

//         void finalizeResources() {
//             if (this.networkResources != null) {
//                 try {
//                     this.networkResources.forceClose();
//                 } finally {
//                     this.networkResources = null;
//                 }
//             }
//         }
//     }

//     public static Thread getThread() {
//         return threadRef;
//     }
// }
